feat(api): don't return a payload on file delete (#1640)

# What does this PR do?

This is to stay consistent with other APIs.

This change registers files in API, even though there are still no
providers. Removing tests that require a provider existing for a merged
API to enable it in API layer.

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan
[Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.*]

[//]: # (## Documentation)

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

docs/_static/llama-stack-spec.yaml

@@ -557,10 +557,6 @@ paths:
       responses:
         '200':
           description: OK
-          content:
-            application/json:
-              schema:
-                $ref: '#/components/schemas/FileResponse'
         '400':
           $ref: '#/components/responses/BadRequest400'
         '429':
@@ -4286,39 +4282,6 @@ components:
       title: FileUploadResponse
       description: >-
         Response after initiating a file upload session.
-    FileResponse:
-      type: object
-      properties:
-        bucket:
-          type: string
-          description: >-
-            Bucket under which the file is stored (valid chars: a-zA-Z0-9_-)
-        key:
-          type: string
-          description: >-
-            Key under which the file is stored (valid chars: a-zA-Z0-9_-/.)
-        mime_type:
-          type: string
-          description: MIME type of the file
-        url:
-          type: string
-          description: Upload URL for the file contents
-        bytes:
-          type: integer
-          description: Size of the file in bytes
-        created_at:
-          type: integer
-          description: Timestamp of when the file was created
-      additionalProperties: false
-      required:
-        - bucket
-        - key
-        - mime_type
-        - url
-        - bytes
-        - created_at
-      title: FileResponse
-      description: Response representing a file entry.
     EmbeddingsRequest:
       type: object
       properties:
@@ -4830,6 +4793,39 @@ components:
       title: URIDataSource
       description: >-
         A dataset that can be obtained from a URI.
+    FileResponse:
+      type: object
+      properties:
+        bucket:
+          type: string
+          description: >-
+            Bucket under which the file is stored (valid chars: a-zA-Z0-9_-)
+        key:
+          type: string
+          description: >-
+            Key under which the file is stored (valid chars: a-zA-Z0-9_-/.)
+        mime_type:
+          type: string
+          description: MIME type of the file
+        url:
+          type: string
+          description: Upload URL for the file contents
+        bytes:
+          type: integer
+          description: Size of the file in bytes
+        created_at:
+          type: integer
+          description: Timestamp of when the file was created
+      additionalProperties: false
+      required:
+        - bucket
+        - key
+        - mime_type
+        - url
+        - bytes
+        - created_at
+      title: FileResponse
+      description: Response representing a file entry.
     Model:
       type: object
       properties: